ShortPoint Add-In: Sorry, there was a problem with ShortPoint Online

Accessing referenced file ........./ShortPoint is not allowed because the reference is outside of the App Web

The Reason:

This is a known SharePoint related issue. Somebody in your organization, change the master page on the root web and checked the box to reset all subsites as well. Changing master pages on root and all subsites automatically will break the installed add-ins.